fix(P0-02): 积分榜改为追加快照(append-only) + available_at cutoff

去掉 uq_standings_league_season_team,改为 (league, season, team, available_at) 唯一;
每次采集 INSERT 新行(available_at=now),ON CONFLICT DO NOTHING,不覆盖旧行。

standings_slice(before):DISTINCT ON (team_id) WHERE available_at<=cutoff
ORDER available_at DESC;before=None → cutoff=now()。
公开 list_standings 取每队最新可用快照(子查询 max available_at)。

迁移 0023 + 切片/路由/docs 同步;测试 test_p0_standings_cutoff(5/5)。
284 测试全绿。

src/api/routes/matches.py

@@ -286,7 +286,9 @@ async def list_standings(
 ):
     """联赛积分榜(只读)。按联赛分组,每张榜按 position 排序。
 
-    season 为空时返回每个联赛最新采集到的赛季榜单(适合前端"查看最新积分榜")。
+    P0-02: standings 为追加快照,公开接口取每队 available_at 最新快照
+    (league_id, season, team_id 上按 available_at 取最新)。
+    season 为空时返回每个联赛最新采集到的赛季榜单。
     """
     # 取每个联赛最新赛季(当 season 为空时)
     latest_seasons: dict[int, str] = {}
@@ -299,9 +301,25 @@ async def list_standings(
         ).all()
         latest_seasons = {r.league_id: r.latest for r in rows}
 
+    # P0-02: 子查询取每队最新 available_at 快照,再 JOIN 回主表拿完整行 + League
+    latest_per_team = (
+        select(
+            Standing.league_id, Standing.season, Standing.team_id,
+            func.max(Standing.available_at).label("max_available"),
+        )
+        .group_by(Standing.league_id, Standing.season, Standing.team_id)
+        .subquery("latest_per_team")
+    )
     q = (
         select(Standing, League)
         .join(League, League.id == Standing.league_id)
+        .join(
+            latest_per_team,
+            (Standing.league_id == latest_per_team.c.league_id)
+            & (Standing.season == latest_per_team.c.season)
+            & (Standing.team_id == latest_per_team.c.team_id)
+            & (Standing.available_at == latest_per_team.c.max_available),
+        )
         .order_by(League.name.asc(), Standing.position.asc())
     )
     if league: